1. Field of the Invention
The present invention relates to a magnetic recording medium. More particularly, the present invention relates to a magnetic recording medium and a process for its production, wherein a backing layer is formed on a thin film-type magnetic recording medium having a thin ferromagnetic metal (inclusive of alloy) layer formed on a substrate of e.g. polyester by electroplating, chemical plating, vapour deposition, sputtering, ion plating or the like, to reduce the frictional coefficient and to minimize the curling, whereby the dropout can be minimized.
2. Description of the Prior Art
Recently, magnetic tapes have been widely used in the fields of audio and video recording, computers, etc. The amount of information to be recorded on magnetic recording media increases year after year, and there is an increasing demand for recording media to have a high recording density.
A thin ferromagnetic metal layer formed by electroplating, chemical plating, vacuum deposition, sputtering or ion plating, is composed of 100% metal or alloy, and thus is capable of having a high recording density. However, when a thin ferromagnetic metal layer is formed by such a method, the surface condition of the substrate gives a substantial effect on the surface condition of the thin ferromagnetic layer.
In order to minimize the spacing loss with the magnetic head, the surface of the magnetic layer is desired to be as smooth as possible, and, at the same time, deposition of foreign matters should be avoided to minimize the dropout. In the case of a thin metal layer, the surface property is much improved over the magnetic layer composed of magnetic metal powder dispersed in a binder. However, since the surface roughness is as small as 0.01 .mu.m (as a R.sub.20 value, i.e. an average value of 20 measured values, at a cut off of 0.17 mm by the Tallistep method mentioned hereinafter), the contacting surface area is correspondingly large and the frictional coefficient is likewise large, whereby smooth running tends to be difficult. Besides, there is a trend that the thickness of the substrate such as a plastic base film made of e.g. polyethyleneterephthalate, polyethylenenaphthalate, polyimide or polyamide, becomes thinner. At present, a thickness of 11 .mu.m or less is being studied. As the base film becomes thinner, the medium tends to be so flexible that the friction will increase, the winding up adhesion is likely to take place, and the adhesion to the guide rollers or support pins is likely to occur. Further, the thin magnetic metal layer tends to curl the medium.
Not only that, when the surface smoothness is so superior as mentioned above, even a very small spacing formed by deposition of very fine foreign matters, is likely to cause dropout.